Dry-mixed mortar is made by physically mixing redispersible latex powder with other inorganic adhesives and various aggregates, fillers and other additives. When the dry powder mortar is added to the water and stirred, under the action of the hydrophilic protective colloid and mechanical shear force, the latex powder particles can be quickly dispersed into the water, which is enough to fully form the redispersible latex powder into a film.
The composition of the latex powder is different, which will affect the rheology and various construction properties of the mortar. The affinity of latex powder to water when it is redispersed, the different viscosities of latex powder after dispersion, the influence on the air content of mortar and the distribution of air bubbles, the interaction between latex powder and other additives, etc., make different latex powders have increased fluidity. , Increase thixotropy, increase viscosity and so on.
After the freshly mixed mortar containing latex powder dispersion is formed, with the absorption of water by the base surface, the consumption of hydration reaction, and the volatilization to the air, the water will gradually decrease, the particles will gradually approach, the interface will gradually blur, and gradually merge with each other, and finally aggregate film forming. The process of polymer film formation is divided into three stages.
In the first stage, the polymer particles move freely in the form of Brownian motion in the initial emulsion. As the water evaporates, the movement of the particles is naturally more and more restricted, and the interfacial tension between water and air forces them to gradually align together.
In the second stage, when the particles come into contact with each other, the water in the network evaporates through capillary tubes, and the high capillary tension applied to the surface of the particles causes the deformation of the latex spheres to fuse them together, and the remaining water fills the pores, and the film is roughly formed.
The third, final stage enables the diffusion of polymer molecules into a true continuous film. During film formation, isolated mobile latex particles consolidate into a new film phase with high tensile stress. Obviously, in order to enable the redispersible latex powder to form a film in the hardened mortar, it is necessary to ensure that the minimum film forming temperature is lower than the curing temperature of the mortar. .
It is generally believed that the redispersible latex powder improves the workability of fresh mortar: the latex powder, especially the protective colloid, has an affinity for water and increases the viscosity of the slurry and improves the cohesion of the construction mortar. In the mortar, it is to improve the brittleness, high elastic modulus and other weaknesses of the traditional cement mortar, and to endow the cement mortar with better flexibility and tensile bond strength, so as to resist and delay the generation of cement mortar cracks. Since the polymer and the mortar form an interpenetrating network structure, a continuous polymer film is formed in the pores, which strengthens the bonding between the aggregates and blocks some pores in the mortar, so the modified mortar after hardening is better than cement mortar. There is a big improvement.